The invention relates to a method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, including both a leading end of a dressing and a trailing end of a dressing. The invention, furthermore, relates to a device for holding and tensioning a cylinder dressing on a printing-machine cylinder, the device having a first arm for holding a first end of a dressing, a second arm for holding a second end of the dressing, and a cam member rotatable for adjusting the first and second arms.
Such a method can be performed, for example, by the device described heretofore in the published German Patent Document DE 42 22 332 C2, the cylinder dressing being tensioned and relieved of tension simultaneously at the leading edge and trailing edge thereof due to the construction of this device. The cylinder dressing in the form of a rubber blanket can be displaced relative to the original position thereof on the jacket of a printing-machine cylinder. For this purpose, the rubber blanket is relieved of tension at the leading edge and the trailing edges thereof by an actuating drive, a toothed quadrant clamping being released at a tension spindle, and the latter being rotated an adjusting travel distance.
Proceeding from this state of the prior art, it is an object of the invention to provide an improved method for tensioning and positioning a cylinder dressing on a printing machine cylinder.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, wherein both a leading dressing end and a trailing dressing end of the cylinder dressing are tensioned, which comprises, in a first step, tensioning both dressing ends, and in a second step, relieving the tension in a first of the two dressing ends, while retensioning a second of the dressing ends.
In accordance with another mode of the method of the invention, the first of the two dressing ends is the leading dressing end, and the second of the two dressing ends is the trailing dressing end.
In accordance with a further mode, the method of the invention, comprises successively tensioning the dressing ends in the first step.
In accordance with an added mode, the method of the invention comprises initially tensioning the trailing dressing end, and subsequently tensioning the leading dressing end in the first step.
In accordance with an additional mode, the method of the invention comprises tensioning both of the dressing ends simultaneously in the first step.
In accordance with another aspect of the invention, there is provided a device for holding and tensioning a cylinder dressing on a printing-machine cylinder, the device having a first arm for holding a leading dressing end of the cylinder dressing, and a second arm for holding a trailing dressing end of the cylinder dressing, and a rotatable cam member for adjusting the first and second arms, comprising a first tension lever pivotable about a first rotary joint, and a second tension lever pivotable about a second rotary joint, the first arm being formed on the first tension lever, and the second arm being formed on the second tension lever.
In accordance with another feature of the invention, the tension levers are loaded by altogether at least one spring.
In accordance with a further feature of the invention, the first rotary joint and the second rotary joint are disposed coaxially with one another.
In accordance with an added feature of the invention, the rotary joints are disposed so as to be offset eccentrically relative to an axis of rotation of the printing-machine cylinder.
In accordance with an additional feature of the invention, at least one spring extends through the first rotary joint and through the second rotary joint.
In accordance with yet another feature of the invention, the at least one spring is a torsion bar spring.
In accordance with yet a further feature of the invention, the tension levers are formed as rockers, and each of the rockers has a first rocker arm for holding the cylinder dressing, and a second rocker arm actuatable by the cam member.
In accordance with yet an added feature of the invention, the device includes a respective roller engageable by the cam member being mounted rotatably in each of the second rocker arms.
In accordance with yet an additional feature of the invention, the tension levers, respectively, carry a clamping device for holding the cylinder dressing.
In accordance with a concomitant aspect of the invention, there is provided a printing machine having at least one device for positioning and tensioning a cylinder dressing having at least one of the foregoing features.
Thus, the method for positioning and tensioning a cylinder dressing on a printing-machine cylinder, which includes tensioning both a front or leading dressing end and a rear or trailing dressing end, is distinguished in that, in a first method step, the two dressing ends are tensioned and, in a second method step following the first method step, a first dressing end of the two dressing ends is relieved of tension or detensioned, and a second dressing end of the two dressing ends is retensioned.
The cylinder dressing can be displaced in circumferential direction on the circumferential surface of the cylinder in this simple way, in practice the first dressing end being pushed and the second dressing end being pulled in the tensioning direction of the second dressing end. In relation to the tension of the first dressing end achieved in the first method step, often only partial detensioning or relief of tension is necessary in the second method step. The detensioning of the first dressing end may commence either before the retensioning of the second dressing end or simultaneously therewith. In both cases, the second dressing end is retensioned during the detensioning of the first dressing end.
Certain cylinder dressings have to be tensioned, in practice, by pulling on both dressing ends in tensioning directions opposite to one another, so that the cylinder dressings can be tensioned so as to rest tautly on the cylinder. The need for tensioning these cylinder dressings at both ends is due to friction between the cylinder dressing and the supporting surface of the cylinder, this friction being comparable to rope friction and being capable of being overcome only by pulling on both ends.
The method according to the invention is based on the assumption that even cylinder dressings to be tensioned in this way can be displaced on the circumferential surface of the cylinder if displacement is preceded by tensioning at both ends. It is assumed that, during clamping, disruptive deformations of the cylinder dressing play a part, as well as the rope friction-like effect. Often permanent deformations become noticeable, particularly after lengthy use and the associated repeated clamping and removal of the cylinder dressing on and off the cylinder. Such deformations can be eliminated by taut tensioning at both ends which precedes displacement, so that the cylinder dressing can subsequently be displaced, and exactly positioned, on the circumferential surface of the cylinder more easily than has been assumed hitherto.
Preferably, a leading dressing end corresponds to the first dressing end and a trailing dressing end to the second dressing end, so that, in the second method step, the leading dressing end is at least partly detensioned, and the trailing dressing end is retensioned. By the leading or front dressing end there is meant that end which, when the printing-machine cylinder carrying the cylinder dressing rolls in operative contact with or on a further printing-machine cylinder, is guided first past the further printing-machine cylinder during each revolution. In the event that the printing-machine cylinder is a plate cylinder for applying a printing ink or a varnish to a print carrier and the other printing machine cylinder is an impression cylinder guiding the print carrier, the so-called print start of the printing or varnishing plate is located at the front or leading dressing end.
In a mode of the method according to the invention, in the first method step, the dressing ends are tensioned in succession. Preferably, in the first method step, first the trailing dressing end and subsequently the leading dressing end can be tensioned.
In a further mode of the method, in the first method step, both dressing ends are tensioned simultaneously.
A device constructed as described in the introduction hereto is illustrated, for example, in FIGS. 1 to 3 of the published German Patent Document DE-OS 23 28 985. In this device, the arms are not formed as tension levers, respectively, pivotable about a rotary joint, but are each movable about a bending point of a U-shaped spring. The arms are also not loaded by a spring, but are themselves resiliently elastic and are parts of the U-shaped spring.
One disadvantage of this heretofore known device is that the printing plates cannot be aligned exactly in position by this device because, depending upon the expandability of the particular type of clamped printing plate, the arms bend to a greater extent at one time and to a lesser extent at another time. In conjunction therewith, there is also the comparatively low tensioning action which can be achieved by the U-shaped spring. Moreover, the method according to the invention cannot be performed by this device, because, as a consequence of design, always only one dressing end is tensioned by an arm, while the other dressing end is held fixedly in location on the printing-plate cylinder.
Proceeding from this state of the prior art, it is thus an object of the invention, furthermore, to provide a device for holding and tensioning a cylinder dressing on a printing machine cylinder, that can be operated conveniently and be suitable, in particular, for performing the method according to the invention.
This object is achieved, according to the invention, by providing the device for holding and tensioning a cylinder dressing on a printing-machine cylinder, with a first arm for holding a leading dressing end and a second arm for holding a trailing dressing end, and with a rotatable cam part for adjusting the two arms, in particular for performing the method according to the invention, which is distinguished in that the first arm is formed on a first tension lever pivotable about a first rotary joint and the second arm is formed on a second tension lever pivotable about a second rotary joint.
By the cam member, there is meant, for example, a control shaft with two cams which are seated on the shaft so as to be offset relative to one another in the axial direction of the latter, a first cam thereof serving to adjust the first arm, and a second cam the second arm. By the cam member, there is likewise meant a control shaft with a cam disk seated on the latter, the cam disk adjusting both the first arm and the second arm. An eccentric shaft functionally identical to the above variants and profiled correspondingly is also such a cam member. It is essential that the two arms be adjustable in succession and/or simultaneously as a result of a rotation of the cam member about the axis thereof which preferably extends axially parallel to the axis of rotation of the cylinder.
When compared with the device belonging to the prior art represented by the aforementioned published German patent Document DE-OS 23 28 985, the device according to the invention has the advantage that cylinder dressings can be aligned precisely in position by the device according to the invention. In the device according to the invention, the arms may be rigid, so that the cylinder dressing held on the arms can be positioned, irrespective of the expandability thereof, by an appropriate adjustment of the arms.
An improved embodiment of the device according to the invention is distinguished in that the tension levers are loaded by altogether at least one spring.
In this case, each tension lever may have assigned thereto at least one spring transmitting the tensioning force to the tension lever. Each of these springs may be supported on the basic cylinder body, in which the tension levers may be mounted via the rotary joints. Preferably, at least one spring bracing the two tension levers relative to one another may also be provided. In this case, the tension levers may form, together with the spring acting therebetween, a tension unit adjustable substantially in the circumferential direction relative to the basic cylinder body without any variation in the tensioning force for tensioning the cylinder dressing. By the one spring or the plurality of springs, substantially higher tensioning forces can be generated than is possible with resiliently constructed arms. Due to the rigidity of the arms, the stability of the tensioning device as a whole increases and distortion-free tensioning of the cylinder dressing can be performed very effectively.
A further embodiment is distinguished in that the first rotary joint and the second rotary joint are arranged coaxially to one another.
This affords possibilities, advantageous in terms of construction, for the at least one spring loading the tension levers to be arranged coaxially with the joints. In a first variant or alternative embodiment, one of the rotary joints may be seated concentrically on the other rotary joint. In a preferred second variant, the rotary joints are arranged so as to be offset relative to one another in the axial direction thereof. For example, according to the second variant, a joint bushing, which is fastened to the respective tension lever and which is rotatable on a joint pin, may be seated on each of the two ends of the latter. Between the joint bushings, a leg spring applying the tensioning force may be wound helically around the joint pin, the leg spring being supported with each of the two legs thereof, respectively, on one of the tension levers and bracing the latter relative to one another. The common central axis of the rotary joints may correspond to the axis of rotation of the printing-machine cylinder both in the first variant and in the second variant.
A further embodiment is distinguished in that the rotary joints are arranged so as to be offset eccentrically relative to an axis of rotation of the printing-machine cylinder.
The advantage of this embodiment is that an advantageous division of construction space in the cylinder interior is achieved. The rotary joints of the tension levers, the rotary joints being offset eccentrically relative to the axis of rotation of the cylinder, may be arranged so as to be offset relative to one another, the joint axes extending axially parallel to one another and axially parallel to the axis of rotation of the cylinder. Preferably, the rotary joints are arranged coaxially with one another, the common axis of rotation being arranged so as to be offset eccentrically and so as to be axially parallel to the axis of rotation of the cylinder.
A further embodiment is distinguished in that a single spring or a respective spring extends through the first rotary joint and through the second rotary joint.
In this case, the joint pins of the rotary joints may be formed as tubular hollow bodies, respectively, whereon the tension levers, for example, carried by joint bushings, are seated. The spring may be inserted into the hollow bodies in a formlocking connection with the hollow bodies, that is fixed against rotation. In this regard, it is noted that a formlocking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a forcelocking connection, which locks the elements together by force external to the elements. In an alternative embodiment, a common joint pin of both rotary joints, whereon the tension levers are seated rotatably, may be formed as a single tubular hollow body through which the spring extends.
A further embodiment is distinguished in that the spring or the respective spring is a torsion bar spring.
By a torsion bar spring, high tensioning forces of, for example, 8 kN for tensioning a varnishing blanket or 12 kN for tensioning a varnishing plate can be applied, the torsion bar spring taking up only comparatively little construction space. In specific applications, one or more compression springs constructed, for example, as helical springs may also be used for bracing the tension levers relative to one another.
A further embodiment is distinguished in that the tension levers are formed as rockers, and each of the rockers has a first rocker arm holding the cylinder dressing, and a second rocker arm actuatable by the cam member.
The second rocker arms may temporarily come into and out of contact with the cam member due to the actuation of the latter. Preferably, the second rocker arms are held in predominantly permanent bearing contact on the rotating cam member, so that the position of the tension levers is reliably fixed.
A further embodiment is distinguished in that a roller contactable by the cam member is mounted rotatably in each of the second rocker arms.
The rollers can roll on the cam member, so that convenient ease of movement of the adjusting device is afforded and any abrasive wear of the cam member or of the tension levers is avoided.
A further embodiment is distinguished in that the tension levers, respectively, carry a clamping device for holding the cylinder dressing. For this purpose, a clamping device for clamping the leading dressing end may be arranged on the first rocker arm of the first tension lever, and a further clamping device for clamping the trailing dressing end may be arranged on the first rocker arm of the second tension lever. The clampings can be produced and released very quickly, so that an exchange of the cylinder dressing for another cylinder dressing takes up only a little time.
The device can be used in rotary printing machines and, for example, offset printing machines. The printing-machine cylinder may be a coating cylinder for coating the print carrier of a coating unit which is located upline or downline of the printing units of the printing machine and which is equipped with the device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for tensioning a cylinder dressing on a printing-machine cylinder, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.